If those who are sent to draw water begin by drinking themselves, the
army is suffering from thirst.
As Tu Mu remarks: 覩一人三軍可知也 “One may know the condition of a
whole army from the behaviour of a single man.” The 先 may mean
either that they drink before drawing water for the army, or before
they return to camp. Chang Yü takes the latter view. The _T‘ung
Tien_ has the faulty reading 汲役先飮者, and the _Yü Lan_, worse
still, 汲設飮者.